Add camera-permission-denied handling to the access-scanner screen

[Lakes41]

Difficulty: Intermediate
Type: bug

Background
app/access-scanner.tsx implements the QR code scanner screen using expo-camera, which requires runtime camera permission on both iOS and Android.

Problem
It's not clear the scanner screen handles the case where the user denies camera permission (or has previously denied it at the OS level) — a bare expo-camera integration without explicit handling typically shows a blank/broken preview instead of clear guidance.

Expected outcome
When camera permission is denied, access-scanner.tsx shows a clear explanation of why the permission is needed, a button to re-prompt (if the OS allows re-prompting) or deep-link to the device's app settings (if permanently denied), and a way to navigate back without being stuck on a broken screen.

Suggested implementation

• Use expo-camera's permission hook to check current status (granted, denied, undetermined) on screen focus.
• For undetermined, prompt for permission with a short rationale beforehand.
• For denied (especially permanently denied on iOS), show a message with a button linking to system settings (Linking.openSettings()).
• Add a clear "Back" affordance so the user isn't stuck.
• Manually verify on both iOS and Android simulators (permission flows differ slightly between platforms).

Acceptance criteria

• Denied permission shows a clear explanation and a way to open system settings
• Undetermined permission shows a rationale before the OS prompt
• User can always navigate away from the scanner screen
• Verified on both iOS and Android

Likely affected files/directories

• app/access-scanner.tsx

[jchinedu]

Hi! I'd love to work on this issue.

I have experience building mobile applications with React Native and Expo, and I've worked with permission-based features where providing a good user experience is just as important as the functionality itself.

For this issue, I'd make sure the scanner handles every permission state gracefully—prompting users with a clear explanation before requesting access, guiding them to the device settings if permission has been permanently denied, and ensuring there's always a way to navigate back instead of leaving users on a broken screen. I'll also verify the behavior on both Android and iOS since the permission flows differ slightly between platforms.

I'd be happy to take this on and submit a clean, well-tested implementation that follows the project's existing patterns.

[grantfox-oss]

🦊 GrantFox — @jchinedu has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #233)
2. Your PR will be reviewed by the Adamantine-guild maintainers

Good luck! Track your progress on GrantFox.